Construction panels are generally formed from sheet aluminum or steel, and they are frequently webbed on their long sides to provide longitudinal stiffening. The edges of the panels, or their webs, are often formed or developed in special configurations so that panels placed side by side may be interlocked to each other along their edges. Many different configurations of interlocking means have proposed or placed into use. Among them are those shown in U.S. Pat. Nos. 1,198,764; 1,429,400; 1,913,342; 2,019,379; 2,302,949; 3,055,461; 3,100,556; 3,131,794; 3,234,697; 3,276,171; 3,394,524; 3,462,906; 3,481,094; 3,606,718; 3,608,267 and 3,969,866.
Roofing panels are a special form of construction panel. It is desirable that roofing panels be capable of installation on the underside of a roofing framework from below the framework. This circumstance makes many panel interlocking systems impractical or inconvenient for roofing panels, including those which involve rotation of one panel with respect to another in the course of installation, or telescoping of panel edges together, or the use of fastening systems which are exposed or which require access to space above the roofing framework.
Furthermore, it is necessary that a roof formed of roofing panels have sufficient integral strength when assembled to avoid sagging and uneveness even though it is attached to the framework at relatively widely spaced points.